Sterilization by Filtration 



I7S 



Sterilization by Filtration. — ^Liquids that cannot be subjected 

 to heat without the loss of their most important qualities may be 

 sterilized by filtration — i.e., by passing them through unglazed 

 porcelain or some other material whose interstices are sufficiently 

 fine to resist the passage of bacteria. This method is largely 

 employed for the sterilization of the unstable bacterial toxins that 

 are destroyed by heat. Various substances have been used for 

 filtration, as diatomaceous earth (Berkefeld filters), stone, sand, 

 powdered glass, etc., but experimentation has shown unglazed por- 

 celain to be the only reliable filtering material by which to remove 

 bacteria. Even the material, whose interstices are so small as to 

 allow the hquid to pass through with great slowness, is only certain 

 in its action for a time, for after it has 

 been repeatedly used the bacteria seem 

 able to work their way through. To be 

 certain of the efficacy of any filter, the fluid 

 first passed through must be tested by 

 cultivation methods to prove that all the 

 bacteria have been removed. 



The porcelain bougies as well as their 

 attachments must be thoroughly sterilized 

 before use. 



After having been used, a porcelain 

 filter must be disinfected, scrubbed, dried 

 thoroughly, and then heated in a Bunsen 

 burner or blowpipe flame until all the 

 organic matter is consumed. In this 

 firing process the filter first turns black as 

 the organic matter chars, then becomes 

 white again as it is consumed. The por- 

 celain must be dry before entering the fire, 

 or it is apt to crack. 



It should not be forgotten that the 

 filtrate must be received in sterile receivers 

 and handled with care to prevent sub- 

 sequent contamination. 



The filtration of water, peptone solu- 

 tion, and bouillon is comparatively easy, 



but gelatin and blood-serum pass through with great difficulty, 

 and speedily gum the filter. 



III. The Disinfection of Instruments, Ligatures, Sutures, etc. — 

 There are certain objects used by the surgeon that cannot well be 

 rendered incandescent, exposed to dry heat at iso°C., or steamed 

 continuously, or intermittently heated without injury. For these , 

 objects disinfection must be practised. Ever since Sir Joseph Lister 

 introduced antisepsis, or disinfection, into surgery there has been a 

 great struggle for the supremacy of this or that highly recommended 



Fig- 33- — Modern 

 autoclave. 



